PassbandWhat is a passband?Defines the probability of an incoming photon of a particular wavelength being measured.Filters | ||||||||
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< < | The simplest example is that of a red filter on an optical telescope; in principle any red photon (~ 5^12Hz ?) arriving is let through, and any other photons are blocked. | |||||||
> > | The simplest example is that of a red filter on an optical telescope; in principle any red photon (~ 5 x 10^12Hz ?) arriving is let through, and any other photons are blocked. | |||||||
In practice of course it's not that simple. No filter is perfect - in the above example, some red photons will be absorbed by the filter, and some other ones might get through. Also some photons are more red than others, and the filter will not be even handed; photons of one redness will be more or less likely to pass than a photon of another redness: (Example red filter pasband). | ||||||||
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> > | Finally a filter is unlikely to be completely even across its width. | |||||||
Instrument, AtmosphereOther factors influence the probability of a photon being measured - the full chain is given in the Observation Data Model doc (2.8) - depending on where 'incoming' is defined. We can model this set of sequential passbands using a ChainedPassbandHow are we going to model it?From two sides; the interface the Passband object presents to the models that use it, and separately how those objects might be defined.Assumptions
ReferencesPublic InterfaceA passband presents the following to the world: | ||||||||
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< < | getPassrate(wavelength) - returns the probability (0-1) of an incoming photon of the given wavelength being measured. | |||||||
> > | getPassrate( Wave ) - returns the probability (0-1) of an incoming photon of the given wavelength/frequency being measured. [What do you get when you apply a Wave with a significant error? Should we just ignore the accuracy?] | |||||||
getMinWavelength() - returns the wavelength below which no photons will be passed.
getMaxWavelength() - returns the wavelength above which no photons will be passed.
[Do people prefer working in wavelengths or frequencies? Of course the above methods can be duplicated for frequencies, or we can use a Wave datamodel that can be represented as wavelength of frequency - MCH]
getUCD() at least for the early days, as there are UCDs defined for some passbands
getName() for humans. Note that the implementation type will also give information and allow other specific | ||||||||
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< < | getPassband(minWavelength, maxWavelength) - returns a new Passband object based on the old. [Hmm not sure about this one - MCH] | |||||||
> > | getCentralWave() - returns approximate central wavelength/frequency/Wave for convenience. | |||||||
Implementations
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PassbandWhat is a passband?Defines the probability of an incoming photon of a particular wavelength being measured.FiltersThe simplest example is that of a red filter on an optical telescope; in principle any red photon (~ 5^12Hz ?) arriving is let through, and any other photons are blocked. In practice of course it's not that simple. No filter is perfect - in the above example, some red photons will be absorbed by the filter, and some other ones might get through. Also some photons are more red than others, and the filter will not be even handed; photons of one redness will be more or less likely to pass than a photon of another redness: (Example red filter pasband).Instrument, AtmosphereOther factors influence the probability of a photon being measured - the full chain is given in the Observation Data Model doc (2.8) - depending on where 'incoming' is defined. We can model this set of sequential passbands using a ChainedPassbandHow are we going to model it?From two sides; the interface the Passband object presents to the models that use it, and separately how those objects might be defined.Assumptions
ReferencesPublic InterfaceA passband presents the following to the world:getPassrate(wavelength) - returns the probability (0-1) of an incoming photon of the given wavelength being measured.
getMinWavelength() - returns the wavelength below which no photons will be passed.
getMaxWavelength() - returns the wavelength above which no photons will be passed.
[Do people prefer working in wavelengths or frequencies? Of course the above methods can be duplicated for frequencies, or we can use a Wave datamodel that can be represented as wavelength of frequency - MCH]
getUCD() at least for the early days, as there are UCDs defined for some passbands
getName() for humans. Note that the implementation type will also give information and allow other specific
getPassband(minWavelength, maxWavelength) - returns a new Passband object based on the old. [Hmm not sure about this one - MCH]
Implementations
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